design element in Worker::batch_size
- old design: setting the batch_size for a worker changed the batch_size for
  all workers by updating the analysis_stats.batch_size of the corresponding
  analysis. Although this code was never triggered in the current system, it
  could have caused potential problems for future developers.
Now setting the batch_size explicitly for a worker only effects the
batch_size for that Worker instance. If it has not been set, the Worker pulls
the batch_size from the analysis_stats record and optionally autocalcs from
avg_msec_per_job if the batch_size<=0.